Mobile communications devices such as mobile phones and personal digital assistants (PDAs) suffer from a shortage of good text input interfaces which restricts the usability of many applications on such devices. For example, consider browsing the internet using a mobile phone; it is difficult for users to manually input search strings and HTTP addresses because of the small number and small size of keys typically available on a mobile phone.
Other approaches for text input on such mobile communications devices have involved using a stylus on a touch screen. However, this requires the provision of an expensive touch screen and the stylus is often difficult to use because of its small size and the small size of the display screen on the mobile device. In addition, any stylus-based user interaction requires the use of two hands at the same time. Thus mobile phones and other hand-held communications devices often do not have a touch screen.
Scanner devices which take the form of a pen and which capture words by moving the tip of the scanner over a printed text are also known. However, these are connected to a stationary computer by means of a cable and are thus not suited for use with mobile communications devices. The pen scanners are not integral with the computer and so may easily be misplaced. Also, pen scanners are not widely available in comparison with mobile phones.